Recently, along with the propagation of portable terminals, the use of visual multimedia contents such as moving pictures, games, photographs, e-Book or the like using potable terminals explosively increases. In order to express such contents more realistically and graphically, terminals equipped with high-quality displays are put into the market, and the display size also tends to increase. However, conventional potable terminals need a space for an input interface of the terminals such as key buttons and a keypad, and therefore there is a limit in increasing the display size.
If a touch-type interface is used, the above problem can be solved. However, if the touch screen is used, the screen may be damaged due to fingerprints or scratches, and if such damages are repeatedly generated, the sensitivity of the touch region is also deteriorated, which may make the touch screen give input signals inappropriately.
Therefore, there is needed a scheme which may replace an existing input interface without touching a screen.